Staying up late every night and sleeping in is a habit that could put people at risk for gaining weight. People who go to bed late and sleep late eat more calories in the evening, more fast food, and fewer fruits and vegetables and weigh more than people who go to sleep earlier and wake up earlier, according to a new Northwestern Medicine study.
Late sleepers consumed 248 more calories a day, twice as much fast food, and half as many fruits and vegetables as those with earlier sleep times, according to the study. They also drank more full-calorie sodas. The late sleepers consumed the extra calories during dinner and later in the evening when everyone else was asleep. They also had a higher body mass index, a measure of body weight, than normal sleepers.
The study is one of the first in the United States to explore the relationship between the circadian timing of sleeping and waking, dietary behavior, and body mass index. The study was published online in the journal Obesity and is expected to appear in a late summer print issue.
"The extra daily calories can mean a significant amount of weight gain—two pounds per month—if they are not balanced by more physical activity," said co-lead author Kelly Glazer Baron, a health psychologist and a neurology instructor at Northwestern University Feinberg School of Medicine.
"We don’t know if late sleepers consume the extra calories because they prefer more high-calorie foods or because there are less healthful options at night," said co-lead author Kathryn Reid, research assistant professor in neurology at the Feinberg School.
The study shows not only are the number of calories you eat important, but also when you eat them—and that’s linked to when you sleep and when you wake up, noted senior author Phyllis Zee, MD, professor of neurology and director of the Sleep and Circadian Rhythms Research Program at Feinberg and medical director of the Sleep Disorders Center at Feinberg and Northwestern Memorial Hospital.